The invention relates to a casting alloy of the AlMgSi type. Also within the scope of the invention is the use of the casting alloy for pressure diecasting, rheocasting and thixocasting, the use of the casting alloy for manufacturing large area and thin-walled components with a high capacity for absorbing kinetic energy by plastic deformation and the use of the casting alloy for manufacturing a component in the form of a safety element in automobile manufacture.
By using modern casting methods it is possible to produce components made of an aluminum alloy which can bear high loads. The aluminium alloys employed, however, must meet a number of requirements. One essential requirement defining the suitability of an alloy is the ability to satisfy specific mechanical properties. Certain minimum values of yield strength and tensile strength determine the load bearing capacity of a structure. In vehicle manufacture there is the further requirement that components that are bent as a result of collision should, prior to fracture, absorb as much energy as possible by plastic deformationxe2x80x94which calls for high ductility in the material selected. Under large series production conditions, it is possible to produce thin-walled castings in a cost favourable manner using pressure diecasting, rheocasting and thixocasting methods i.e. in a form for use as crash-relevant components in automobile manufacture. Thin walled parts place high demands on castability. Aluminum alloys able to provide the required flow behaviour or mould filling capacity are mainly those alloys with a eutectic containing silicon.
An AlMgSiMn alloy that is suitable for diecasting, rheocasting and thixocasting safety components for the automobile industry is known from EP-A-0 792 380. The alloy exhibits a magnesium excess compared with the composition corresponding to the quasi-binary eutectic. As a result of the high manganese content, sticking in the mould is avoided and the ease of removal from the mould is good. Apart from that, the alloy has a very low iron content.
Components with wall thicknesses that are in some cases small, such as those employed as structural parts in automobile manufacture, tend to distort on quenching with water and must, therefore, subsequently undergo complicated straightening operations. Also, residual gas porosity and a high solution treatment temperature can lead to blisters at the surface of the component. In the production of components of the kind mentioned above using pressure diecasting, rheocasting and thixocasting attempts are made, therefore, to meet the minimum strength and elongation values without high temperature solution treatment and subsequent water quenching.
For crash-relevant components in automobile manufacture the emphasis is placed on ductility i.e. formability and on ductile failure expressed by the elongation at fracture. The strength, expressed by the yield strength, can thereby be relatively low.
The object of the invention is to specify an aluminum alloy by means of which a high elongation at fracture can be reached with adequate yield strength, also without performing high temperature solution treatment and subsequent water quenching.
The foregoing object is achieved by way of the invention by providing a casting alloy of the AlMgSi type containing:
and aluminum as the balance along with production related impurities, individually at most 0.02 wt. %, (weight-%) in total at most 0.2 wt. %, and with the further provision that the magnesium and silicon are present in the alloy in a Mg:Si weight ratio of 1.7:1, corresponding to the quasi binary eutectic made up of the phases Al and Mg2Si, whereby the deviation from the exact composition of the quasi-binary eutectic amounts to at most xe2x88x920.5 to +0.3 wt. % for magnesium and xe2x88x920.3 to +0.5 wt. % for silicon.